A build of Android from a non-profit organisation known as Linaro who specialize in software for ARM (the type of chip you’re more than likely running on your Android device(s)) can nearly double the performance of Android AOSP.
Here’s a video which shows you android AOSP on a BeagleBoard (an open-source board, similar to Raspberry Pi, but more expensive) vs Linaro Android which has lots of tiny optimizations on the CPU code to make it run really fast.
Linaro say that Google love to innovate and create all of the new fancy features, while they can optimize the software to run really really well on devices other than the Nexus range. The Linaro Android builds on some boards, but if this were merged into AOSP/CM9 we’d see many more devices without many people actually noticing.
The optimizations are to all areas of Android including Bionic (Google’s standard library replacement) and even to the compiler used to Linaro’s own which is optimized for ARM (and they are even sponsored by ARM themselves!). In Android, there’s a huge need for optimization due to the stack and the use of Java (which is well known for consuming resources in mass amounts, but running slowly).
The Optimizations are already submitted to CM9’s gerrit and hopefully we can see this merged back into AOSP so there work will be seen by Jellybean/next Android version.